It's not a work of historical fiction. It is not reality. It is a work of fantasy. It doesn't have to be accurate
You misunderstand. I (and Brin) are not criticizing 300
for not being historically accurate; we are criticizing it for possessing particular inaccuracies that advance an authoritarian, militaristic agenda.
It's not inaccuracy that is bad, it's inaccuracy in the service of an immoral agenda that is bad.